Detection Technology in Operation of Suspension Composite Insulators

    01, overview

    With the development of the power industry, the transmission capacity has increased sharply, and the voltage level has been continuously improved. 110, 220, 500, 750 and even 1000 kv have emerged and matured. The power system has higher and higher requirements for insulators, and new insulators are also emerging. Previously, porcelain insulator XP series, glass insulator LXP series, now anti-fouling porcelain insulator XWP series, tempered glass insulator FC, BC, etc., have various performances. Compared with synthetic insulators, the composite insulators stand out because of their light weight, high mechanical strength, low maintenance workload, good antifouling performance and low cost.

    Synthetic insulators are called organic composite insulators, silicone rubber composite insulators.

    Composite insulators can be divided into models according to model and different manufacturers: HXS series (Baoding products) FXBW series (Wenzhou Guogong, Hubei Xiangfan, Guangzhou,) FXB series (Shandong Zibo, Shanghai Hongqiao, Dalian Electromagnetic Factory) XSH series (Xiangfan, Hubei) and many more.

    In our Yuncheng transmission line, the voltage level can be divided into 110kv, 220kv, 500kv.

    (This article discusses the line rod suspension composite insulator)

    The basic structure of the composite insulator is a metal fitting, a core rod, and a shed skirt.

    The mandrel is the bearing part of the mechanical load of the composite insulator, and at the same time is the main part of the inner insulation. The core rod material of the composite insulator is composed of resin-reinforced glass fiber.

    The shed skirt is the outer insulating part of the composite insulator. Its function is to make the composite insulator have sufficient outer insulation performance against moisture flashing and pollution flashing, and protect the mandrel from external environment. Generally, the shed skirt has excellent resistance. Scatter flash, resistance to tracking and erosion, resistance to high and low temperatures and atmospheric aging. The excellent resistance to flashover of composite insulators is provided by the shed jacket, which is easily damaged on the outer layer of the mandrel, so the shed skirt is also the focus of our protection and research.

    The mandrel and the sheath are joined together by an intermediate bonding layer, which becomes a weak point of the internal insulation if the bonding is not good.

    A metal fitting is a mechanical load connecting member of a composite insulator that is assembled with a mandrel to form a joint of a composite insulator to transmit a mechanical load.

    02, the advantages of composite insulators

    Composite insulators are completely different from ceramic or glass insulators from structure to material. The performance is also very different, mainly the following:

    2.1, high strength, light weight

    Anyone who has been exposed to synthetic insulators knows that a composite insulator is very light, only one-fifth of the porcelain insulator, but the circumferential tensile strength of the insulator is generally higher than 6000mpa, and such advantages are very popular. The welcome of the staff can greatly reduce the labor intensity in construction and accident repair.

    2.2, no zero value

    The composite insulator belongs to a rod-shaped insulating structure, and the shed is an organic polymer structure of silicone rubber. The inner and outer pole pitches are substantially equal, and generally no internal insulation breakdown occurs, so zero value detection is not required.

    2.3, high flashover voltage

    The umbrella skirt of the composite insulator is an organic polymer structure, and the surface energy is very low and exhibits strong water repellency. Hydrophilicity or hydrophobicity is the surface property of a solid material. Water forms a water droplet or water droplet on a hydrophobic solid surface. The familiar surface of the lotus leaf is a typical strong hydrophobic surface in nature. The water has a rounded globular shape on it; and the water forms a continuous water film or water sheet on the hydrophilic surface, such as the state of water on the surface of the ceramic or glass. It does not form a continuous water film, so the leakage current is small, it is difficult to form a local arc, and flashover is not easy to occur. Therefore, the flashover voltage is high.

    2.4, simple operation and maintenance

    High pollution flash performance, no need to carry out dirty cleaning, there is no need to carry out zero value detection, the maintenance workload is greatly reduced

    03. Technical data of composite insulators

    China's synthetic insulators mainly consist of the four series that I introduced earlier. Let me introduce the four series of composite insulators:

    3.1, HXS series

    This series mainly consists of Baoding Repair Factory of North China Power Group Corporation and Hebei Zhengheng Power Equipment Co., Ltd., and the meaning of H X S 2--110/70(100) models:

    H—represents a composite insulator,

    X-- indicates suspension,

    S—represents solid (stick)

    2—represents the design serial number

    110—represents the rated voltage level,

    70—represents the rated mechanical load (kN)

    The total leakage distance is 242cm, structure: the size of the umbrella structure

    Other models of H X S 2--220/160 (100) leakage distance is 484cm, structure: the size of the umbrella structure. H X S 2--500/160 (180) leakage distance is 1100cm, structure: is the size of the umbrella structure.

    3.2

    FXBW series

    The series mainly includes Wenzhou Guogong Industry and Hebei Zhengheng and Xiangfan. The meaning of the FXB W 3-110/70 model:

    FXB—represents a rod-shaped suspension composite insulator;

    W—represents the size of the umbrella (the equal diameter does not indicate);

    3-- indicates the design serial number, 1, 2 means the creepage ratio is 20mm/kv, and 3 and 4 indicate the creepage ratio is 25mm/kv.

    3.3

    XSH series

    This series is mainly produced in Xiangfan, Hubei. The meaning of the model number of XSH-70/110B:

    XSH—represents a series of suspended solid composite insulators;

    70—representing the rated mechanical load (kN);

    110—represents the rated voltage (KV);

    B—represents the structural type.

    3.4

    FXB series

    This is mainly Zhengheng in Hebei, Zibo in Shandong, Xiangfan in Hubei, and Hongqiao in Hubei. It is also the most composite insulator used by us. The meaning of the model of FXB-110/70 is:

    FXB—represents a rod-shaped suspension composite insulator;

    70—representing the rated mechanical load (kN);

    110—represents the rated voltage (KV);

    The insulators of these four factories share 13416 branches. The specific synthetic insulator parameters are detailed in the annex.

    04

    Operation, maintenance and overhaul of conventional insulators for composite insulators

    Composite insulators have been widely used in power systems due to their light weight, high strength, strong resistance to flashover, and ease of manufacturing and maintenance, breaking the long-term dominance of porcelain and glass insulators. According to incomplete statistics, the total number of composite insulators operating in China's power grid is about 2 million. In terms of the quantity used, China has become the second largest country in the use of composite insulators after the United States. However, as the running time and the number of operations increase, the information on the failure of the composite insulator gradually increases. According to incomplete statistics, as of 1998, 15 interface breakdown accidents occurred in East China and North China, and 23 incidents of pollution flashover occurred in Guangdong, East China and North China. Obviously, while improving the formulation and manufacturing process and improving the quality of composite insulators, it is of great significance to carry out research on the operation of composite insulator detection technology to ensure the safe operation of the power grid. At present, the detection technologies of the chief insulators in operation are mainly:

    4.1

    Direct observation

    At present, the most common method for external physical defects of composite insulators is direct observation, that is, using binoculars to observe under the tower to find common surface defects such as sheath, shed, and metal fittings, such as cracking, electric erosion, and chalking. , traces of leakage, etc., if there is any of the above phenomena, the insulation should be replaced immediately. However, the ground observation is not reliable enough, and it is necessary to detect the tower and it is difficult to find the internal insulation fault such as the tree-like channel.

    The specific observations are:

    1) Observing the partial discharge of the surface of the composite insulator under meteorological conditions such as rain, fog and dew

    2) Whether there is obvious slippage and attachment corrosion of the end fittings.

    4.2

    Ultraviolet imaging

    A small but stable surface partial discharge can cause the composite insulator shed and sheath to form carbonized channels or electrical erosion. When the surface of the insulator forms a carbonization channel, its service life is greatly reduced, even in the short term. The electronic ultraviolet optical flaw detector can be used to electrically detect the carbonization channel and the electric erosion formed on the surface of the composite insulator due to partial discharge. The principle is that the charged particles recombine during the partial discharge process, and when the surface of the insulator forms a conductive carbonization channel. Partial discharge is intensified. The disadvantage of this method is that it requires operation at night and in a positive temperature environment; it is also required that partial discharge is occurring at the time of detection, which requires that the detection should be carried out in an environment of high humidity or even rain. However, the detection results are easily affected by the observation degree, and the detection equipment is also expensive.

    This method of detection is only introduced in the Synthetic Insulator Technology Exchange Conference. I have listened to the Chengdu Institute of Synthetic Insulators in Sichuan, but I have not used it. I need to know more.

    4.3

    Ultraviolet imaging

    Infrared imaging method can detect local temperature rise of the edge caused by partial discharge or leakage current flowing through the insulating material, and can be used for line detection. The Foshan Power Supply Branch of the Broadcasting and Television Group conducted a thermal survey of the infrared thermal image of a large number of operating composite insulators. It was found that the insulators with obvious local hot spots have a blackening and chalking on the surface of the silicon rubber of the high-voltage end of the insulator. It becomes brittle and the water repellency is basically lost, and some small cracks or even serious damage appear. The hot point to the high voltage end cannot withstand the power frequency withstand voltage test or the steep wave impact test. It can be seen that the hot spot is the position of the partial discharge progress of the inner insulating valence surface. . The high cost of the instrument and the measurement of the influence of sunlight, wind, moisture, ambient temperature and some factors that can cause abrupt changes in the surface temperature of the insulator are the inadequacies of infrared imaging. It also affects its application.

    I also have an infrared camera in my work area. I have also used synthetic insulators for testing, but the results are not satisfactory.

    4.4

    Ultrasonic method

    Tsinghua University has studied the use of ultrasonic waves to detect composite insulator core rod cracks. The realization of ultrasonic testing is based on the principle that the ultrasonic wave will reflect, refract and change mode at the interface between the two media during the propagation from one medium to another. The ultrasonic generator emits the initial pulse into the insulator medium. The size and position of the defect wave in the insulator can determine the defect in the insulator. Ultrasonic detection of composite insulator mechanical defects has the advantages of simple operation, safety and reliability, strong anti-interference ability, etc. However, due to its coupling, attenuation and ultrasonic transducer performance problems, there has not been a major breakthrough in long-distance telemetry, which is not suitable. On-site inspection, and mainly used for enterprise production online testing and laboratory identification.